1. Field of the Invention
The present invention relates to a structure for sealing debris of a rotating member in an apparatus even when the rotating member rotated at high speed is accidentally broken by a centrifugal force as in a centrifuge.
2. Description of the Related Art
A rotating member used for a centrifuge is provided with a test tube hole for mainly holding a test tube inputted with a sample and a user inserts the sample into the hole and rotates the rotating member at high speed and separates the sample having a small mass difference or density difference by operating a centrifugal force to the sample. At this occasion, the centrifugal force is naturally exerted to the rotating member per se, stresses are generated at inner portions thereof and therefore, there is a concern that the rotating member is broken by the centrifugal force in rotating. Therefore, a fabricator executes design having a sufficient allowance therefore including fatigue of a metal by repeated use and except a case by an error in a method of using the rotating member such as an error in an allowable specific weight of the sample or corrosion of the rotating member by a failure in handling a corrosive sample, breakage in previously determined product life may be regarded to be null.
However, a way of thinking that safety of a user needs to be ensured even when breakage which seems to be impossible to be brought about is brought about, has been promoted in recent years, and according to IEC standards 61010-2-020 ‘Particular requirements for laboratory centrifuges’, an accident which seems to bring about the maximum damage is assumed, a test devised to bring about the accident (MCA test: Maximum Credible Accident) is carried out, and it is requested to guarantee to be safe even thereby. Although conditions of the MCA test differ by a kind of a centrifuge and a rotating member used such as seizure of a bearing, breakage of a shaft, separation of a rotating member from the shaft or the like and cannot be specified sweepingly, in many cases, a breakage of a rotating member by a centrifugal force is selected as an accident which brings about the maximum damage. However, as described above, it is difficult to break a rotating member by normally using the rotating member and therefore, a cut groove calculated to break at the maximum rotational speed to which a selected rotating member can reach is worked to a rotating member 3d as designated by numeral 14 of FIG. 8A to be broken into two. Further, it is evaluated whether debris can be sealed into a main body, whether a guard member for executing sealing operation is cracked, whether the main body is moved in a predetermined range or the like. Therefore, in order to satisfy the standards, in many cases, it is necessary to constitute the above-described centrifuge which is capable of withstanding breakage. Generally, as shown by FIG. 6, a guard cylinder 13 is arranged at an outer periphery of a bowl 4b constituting a rotating chamber 2b for rotating a rotating member as a guard member, and is designed such that even when the rotating member is broken and impacted, debris do not break therethrough. Further, in the case of a centrifuge referred to as cooler attached of a type for making a cooling fluid flow on an outer side of a bowl in order to maintain a temperature of a sample to be separated constant, as shown by FIG. 7, in order to prevent wasteful heat input, it is necessary to provide an insulating layer 11c on an outer side of a bowl 4c and therefore, debris is sealed by providing a guard cylinder 13c further on an outer side thereof.
Next, an explanation will be given of a behavior when a rotating member is broken by taking an example of the MCA test in reference to FIGS. 8A, 8B, FIG. 9. As shown by FIG. 8A, the cut groove 14 designed to be broken at a rotatable maximum rotational speed is worked at the rotating member 3d which can be used in a centrifuge to be evaluated and is provided with a maximum energy in breaking, and the centrifuge is operated at a predetermined rotational speed to be broken by a centrifugal force. As shown by FIG. 8B, a rotating member debris of the rotating member 3d broken in two is provided with a speed component in a tangential direction of a rotational direction and therefore, assuming that the rotating member is broken to separate into two instantaneously by disregarding a behavior of breakage by progress of a crack, respectives thereof are moved radially in arrow mark directions, break through a bowl 4d having a thin wall structure and impacted to a guard cylinder 13d further on an outer side as shown by FIG. 9. At this occasion, much of rotational energy provided to the rotating member (E=½×I×ω2 where I: moment of inertia around axis of rotating member, ω: angular velocity of rotating member) is consumed as local deformation energy and total deformation (deformed into ellipse) energy of the guard cylinder 13d and deformation energy of the rotating member debris 15 per se by the impact and is partially consumed also by heat, sound or the like. On the other hand, the above-described speed components in the tangential direction of the rotating member debris 15 produce a couple moment and therefore, there is also a case in which portions of the moment are conducted to the guard cylinder 13d or the centrifuge integrated with the guard cylinder 13d and a main body of the centrifuge is rotated or moved. Particularly when the guard cylinder 13d is significantly deformed to impinge on or bites a frame 10d constituting an outer frame of the centrifuge, the force of rotating or moving the main body of the centrifuge is more increased to enhance a danger.
From the above-described, sufficient strength and toughness are requested for the guard cylinder used as the guard member in breaking the rotating member such that the guard cylinder is not cracked even when the rotating member is accidentally broken and the debris is impacted thereto and the guard cylinder is deformed as less as possible. A material thereof differs by the maximum rotational energy of the usable rotating member, normally, in a centrifuge capable of using a rotating member having large energy and having large energy in breaking, a heat treatment steel or a tough hardened steel is used and for a centrifuge capable of only using a rotating member having comparatively small energy, a carbon steel tube which is on sale in place of the heat treatment steel or the tough hardened steel and is inexpensive or the like is adopted and necessary strength is adjusted by pertinently selecting a wall thickness thereof. An air gap between the guard cylinder and the outer frame of the centrifuge is determined in consideration that even when the guard cylinder is deformed by impacting debris in breaking, movement of the centrifuge is sufficiently confined into a predetermined range. Further, as shown by JP-A-50-056988, an inner side of a guard cylinder is installed with a member softer than the guard cylinder, energy is consumed by facilitating to deform when debris is impacted and a time period consumed by energy is prolonged to thereby devise to alleviate impact force.